Seismic Behavior of Active Faults Through Multisource Optical Imagery: From Satellite to Drone Resolution (case study: The North Zanjan fault)

Abstract. Detecting and characterizing active faults is crucial for seismic hazard assessment, especially in regions with long earthquake recurrence intervals, such as Iran. Traditional methods, including seismology and geodesy, often fail to identify active faults and assess their seismic potential. This study overcomes these limitations by integrating multi-source datasets with different temporal and spatial resolutions to investigate the North Zanjan Fault (NZF) in the western Alborz Mountains. The NZF is a reverse-dextral fault capable of generating Mw 6.5–7.0 earthquakes. The research employs high-spatial-resolution (HSR) Pleiades Tri-stereo imagery, archival aerial photographs, and RGB overlapping drone-derived imagery to analyze Quaternary geomorphic markers. Photogrammetric techniques are utilized to detect fault traces, map deformed landforms, and reconstruct displacements at multiple scales. By integrating satellite- and archive aerial-derived digital elevation models (DEMs), a detailed 1:5000 scale morpho-structural map is developed, identifying three fault segments connected by thrust fault arrays. Horizontal displacements range from 1.5 to 670 m, while vertical offsets span 1.5 to 77 m. Drone surveys at five locations provide high-resolution data (1:500 scale), revealing an average single-event oblique displacement of 1.10 m. The Sohrein site analysis indicates four Quaternary seismic events, each with an average vertical displacement of 1.30 m. These findings highlight the seismogenic potential of the NZF and demonstrate a scalable methodology for identifying previously unrecognized fault strands, ultimately contributing to improved seismic hazard assessments in the Iranian plateau and similar tectonic environments.